Five states head to the polls on Tuesday. Hillary Clinton and Donald Trump should win most of their respective primaries, but there’s always the potential for surprises. And the "horse race" for delegates comes to life, thanks to HuffPost’s data team. This is HuffPollster for Tuesday, March 15, 2016.

CLINTON ‘MISSED HER CHANCE AT A KNOCK-OUT' - Kyle Kondik and Geoffrey Skelley: “ If Hillary Clinton had won Michigan convincingly, as almost all polls erroneously suggested she would, and then followed up with a March 15 sweep of Florida, Illinois, Missouri, North Carolina, and Ohio, she would have had a compelling case to make that the Democratic contest was effectively over. Now she heads into 'Titanic Tuesday' still holding a commanding position in the race, but the door is open for Sanders to continue fighting for the remainder of the primary season…. Clinton retains big leads in Florida and North Carolina, while Illinois, Missouri, and Ohio have all gotten close. Clinton’s once-big lead in Ohio polls has nearly disappeared, and the state is similar enough to Michigan to raise questions. However, Michigan has a stronger liberal Democratic tradition than Ohio, and Ohio’s Democratic electorate is more dispersed throughout the state than in Michigan…. Ultimately, a Sanders win in Ohio would be a surprise...but not a shocking surprise like Sanders’ win in Michigan was….[Missouri] is probably Sanders’ best shot at a victory.” [ Center for Politics ]

TRAJECTORY OF GOP RACE WILL BECOME CLEARER - More from Kondik and Skelley: “ Yes, many Republicans detest [Donald] Trump, and he does not appear to have anything close to solid majority support in the Republican Party. Yet he still has been getting about 35% or more of the vote in many places...And now, on Tuesday, there are two true winner-take-all contests in Florida and Ohio, in addition to potentially winner-take-most contests in Illinois and Missouri and a proportional delegate race in North Carolina. While unlikely, it is not out of the question that Trump could sweep all five states. And if he does, we don’t see a practical way to stop him from winning the nomination, save for changing convention rules and guaranteeing a massive implosion in the GOP…. March 15 has the potential to be D-Day for the Republican race. Unless someone steps up and defeats Trump. John Kasich in Ohio seems like the best bet to beat Trump anywhere on Tuesday.” [ Center for Politics ]

Marco Rubio likely to falter in Florida - Marc Caputo: “Buried by an avalanche of awful Florida poll numbers, Marco Rubio’s campaign for president has hit the last stage of grief: Acceptance….Barring divine intervention, the cold hard math of the polls will come to bear. The surveys vary wildly, showing Donald Trump with anywhere from a 5- to a 23-percentage-point lead ….Making a Rubio win even more unlikely is that so many Republicans have already cast early and absentee ballots, a record 1.14 million. That’s probably half of the electorate who will vote in the entire primary. So in order for Rubio to have a shot at winning, he’d need to win Election Day by the same margin that he has likely lost the early vote by. Based on the averages of the recent Florida polls, Rubio’s deficit could be as big as 16.5 percentage points. If that’s accurate, it’s a nearly insurmountable lead by Trump: 190,000 ballots heading into Election Day.” [ Politico ]

Winner-take-all delegate rules could still mean a Trump majority, but it’s harder without Florida and Ohio - Nate Cohn: "Whether Mr. Trump can win the 1,237 delegates necessary to avoid a contested convention could easily turn on whether he can win one or both of these states. So far, Mr. Trump has won about 42 percent of delegates — a share that has offered some consolation to his beleaguered opponents. But going forward, Mr. Trump could easily win 60 percent of the remaining delegates between now and June — enough to win the nomination — without doing any better than he has done so far….I f Mr. Trump won at the pace he has so far, based on a demographic model of the race...it would give him nearly 80 percent of the delegates awarded on Tuesday ….Without Ohio, Mr. Trump would probably need to win California — which holds 172 delegates — to get enough delegates to secure the nomination….If Mr. Trump lost both Florida and Ohio, his odds of reaching the 1,237 delegates needed to win would start looking worse….If Mr. Rubio lost Florida and left the race, it could help Mr. Cruz and Mr. Kasich even more in states like California, Maryland and Wisconsin. It might give Mr. Kasich a better chance to nab a few delegates from Mr. Trump along the Eastern Seaboard." [ NYT ]

WHY TUESDAY'S PRIMARIES COULD OFFER SURPRISES - As last week's Michigan's Democratic primary demonstrated, any number of factors can add up to a polling misfire, even in what looks to be a clear-cut contest. Here's what might happen if surveys miss the mark again:

-Late shifts in momentum. Earlier in the year, polling on Iowa's GOP primary largely failed to catch a last-minute move toward Sen. Ted Cruz (R-Texas). Recent national surveys show Marco Rubio's campaign on the downswing , although it's less clear which of his rivals will see the most benefit.

- Faulty turnout assumptions. Michigan's pollsters underestimated the state's record-level turnout, especially among the young voters who comprise Bernie Sanders' base. With Hillary Clinton's lead demonstrably narrowing in states like Ohio and Illinois, a similar miscalculation could cause another upset. That's perhaps a slightly greater possibility in Ohio, where a recent court ruling means that 17-year-olds have the right to vote .

- Strategic voting or voter confusion . While it's hard to say how much of an impact strategic voting plays, there are signs that enough Democrats in Michigan crossed party lines that their absence affected results in their own party. This time, there's also the complication of anti-Trump voting, which led Rubio to suggest recently that his Ohio supporters instead vote for Ohio Gov. John Kasich -- a pitch that could end up giving Kasich a last-minute boost. And not all unusual voting is strategic. Ohioans have expressed concerns about the Republican primary ballot , which lists the field of primary candidates -- including many who've since dropped out -- twice but will count only one section as a valid vote.

- Scarce polling. Some state primaries barely have enough data to be proved wrong or right. In Missouri, for instance, only three polls have been taken of the Republican primary, with just two conducted since the beginning of 2016.

WATCH THE CANDIDATES RACK UP DELEGATES IN THE ‘HORSE RACE’ - Adam Hooper, Hilary Fung, Shane Shifflett, Nicky Forster and Alissa Scheller turned the race for delegates into a literal horse race. See how the race has changed as states have allocated delegates, as well as how superdelegates change the picture. [ HuffPost]

TRUMP CLAIMS TO HAVE INCREASED TURNOUT, BUT HAS HE? - Meghan Keneally: " Until each state holds its respective contest,it’s impossible to tell if Trump’s claim is true. What can be determined, however, are voter registration numbers. At least two of the states that are holding their primaries on Tuesday -- Florida and Illinois -- have seen marked increases in the number of registered voters. According to records from the Florida Department of State, the number of Republicans registered in time to vote in the primary has gone up just over 3 percent since the 2012. Democrats, however, have seen a slight drop during that same period...,.Michael McDonald, an associate professor of political science at the University of Florida, told ABC News that some longtime Democratic districts in Florida... have likely seen an uptick in Republican registrations as a result of the candidates in this race. That said, the specific candidate they feel passionate for won’t be confirmed until Election Day ." [ ABC ]

OBAMA’S RATINGS IMPROVING ON KEY ISSUES - Jim Norman: "More Americans say President Barack Obama is doing a good job of improving the nation's energy policy (48%) and making America prosperous (45%) than at most points in his presidency. On another key measure of his presidency, 54% say Obama is doing a good job of protecting the nation's environment, a slight boost from last year but mostly in line with his recent readings…. The improvement on all three from last year mirrors the improvement in Obama's overall job approval rating , now the best it has been since 2013 ….Almost identical percentages of Democrats give Obama credit for doing a good job on the environment (81%), prosperity (81%) and energy (80%). Only small minorities of Republicans say he is doing a good job on the three, with more variation than among Democrats." [ Gallup ]

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